Russia has deployed 28 fighter jets and bombers to Syria, US officials said. In recent weeks Russia has stepped up its military support for the regime of Syrian President Bashar al-Assad, a move which the US claims will escalate the Syrian civil war.

US officials confirmed reports that military equipment and personnel had been sent to the northern Syrian air base in Latakia, which satellite images obtained last week (14 September) by Foreign Policy magazine showed had undergone significant expansion in recent months.

"There are 28 fighter and bomber aircraft" at the air base, a US official told AFP on condition of anonymity. A second official confirmed the figure, and added that there were also 20 Russian combat and transport helicopters at the base. Russia was also operating drones over Syria, said the second official. Russia has sent 12 SU-24 attack aircraft, 12 SU-25 ground attack aircraft, and four Flanker fighter jets, according to the officials.

Experts believe that Russia intends to launch air strikes against rebel groups, including Islamic State (Isis), battling to oust Assad. Russian President Vladimir Putin has called on the West to back Assad as part of an international 'anti-terror' coalition.

US and Russian defence officials have spoken for the first time since the Ukraine crisis following Russia's military build-up in Syria, with the US conducting its own air strikes against Isis in Syria and Iraq as part of an international coalition.